This invention relates to a theftproof device, and more particularly to a flexible tying member forming part of a theftproof device and through which an optical fiber extends.
A theftproof device for vehicles such as motorcycles has been proposed by the assignee of the present application, which uses a flexible tying member such as a wire cable, through which an optical fiber extends. The proposed theftproof device is used in such a manner that a vehicle, which is to be protected from theft, is tied to a solid structure such an electric pole, by means of the above flexible tying member, while a photo signal is permanently transmitted through the optical fiber. When the flexible tying member is cut in two to cause interruption of the transmission of the photo signal through the optical fiber, the cutting of the flexible tying member is detected in a photoelectric manner to actuate a warning device to give warning
Such flexible typing member with an optical fiber incorporated therein should desirably have such a structure as to fully protect the optical fiber from damage, and also should have sufficient strength so as to withstand frequent use. Further, it should have a moderately small diameter to facilitate its handling, particularly in a limited housing space for a vehicle to be protected from theft. In addition, for normal operation of the theftproof device, the optical fiber should be disposed in the flexible tying member in such a manner as to keep the transmission loss of light through the optical fiber at a small value, as well as to obtain sufficient transmission efficiency of light through the optical fiber.